1. Field of the Invention
The present invention relates to a device for nullifying data to protect its copyright, and in particular relates to techniques for enhancing user convenience while protecting copyrighted data.
2. Related Art
The digitization of information has been increasing in recent years. Since digitized information (hereafter referred to as “digital content”) not only is relatively easy to handle but also does not degrade in quality with time, information such as audio and video data is becoming more and more digitized.
On the other hand, digital content can be copied perfectly with no decrease in quality. This provokes unauthorized acts such as illegal duplication or tampering of copyrighted information.
To discourage such unauthorized acts, a method may be employed that encrypts digital content, and provides a decryption key for decrypting the encrypted digital content (hereafter simply referred to as “encrypted content”) only to devices of authorized users who have agreed to pay a usage fee to the copyright holder.
This prohibits the encrypted content from being decrypted using devices other than those of the authorized users. Hence the digital content can be protected from unauthorized use.
Also, there is a method for indicating the copyright protection status of digital content. According to this method, copy control information (CCI) that shows whether copying of the digital content is permitted or not is attached to the digital content.
In more detail, the copy control information carries one of the four instructions “Copy Never”, “Copy one Generation”, “Copy No more”, and “Copy Free”.
“Copy Never” means no copies of digital content are permitted.
“Copy one Generation” means only a first generation copy of digital content is permitted. The first generation copy of the digital content is given copy control information “Copy No more”.
“Copy No more” is copy control information that is attached to digital content which is a first generation copy of digital content whose copy control information is “Copy one Generation”. “Copy No more” means copying is not permitted any more though it was previously.
“Copy Free” means digital content can be copied freely.
In commercial digital broadcasting and the like, digital content is transmitted via a transmission line in the following manner. If the copy control information of the digital content is “Copy Never”, “Copy one Generation”, or “Copy No more”, it is definitely transmitted in an encrypted form, to ensure security on the transmission line. If the copy control information of the digital content is “Copy Free”, it is usually transmitted in an unencrypted form.
When the user obtains digital content whose copy control information is “Copy Never” via a transmission line and reproduces it, the user is prohibited from copying the obtained digital content to a recording medium. Also, when the user obtains digital content whose copy control information is “Copy one Generation” and records it onto a recording medium thereby generating digital content whose copy control information is “Copy No more”, the user cannot copy the digital content recorded on the recording medium to another recording medium. In such cases where copying of digital content is completely prohibited, the user is likely to encounter a lot of inconveniences.
If copying of digital content transmitted via a transmission line is permitted, the user can perform time shifting, i.e., the user can record the digital content to a recording medium for later reproduction, or the user can record the digital content to a recording medium such as an HDD (hard disk drive) and at the same time reproduce it. However, in the case of digital content marked as “Copy Never”, once the user breaks off viewing the digital content to go to the bathroom or to answer the telephone or doorbell, he or she cannot view the missed part unless the digital content is rebroadcast. Many movie films run for about two hours, and some feature length films even run for more than four hours. Also, commercial digital broadcasting and the like are usually commercial-free. Therefore, to view an entire movie film or the like which is marked as “Copy Never”, the user cannot answer the phone or doorbell and cannot even go to the bathroom for the running time of the movie film that lasts two to four hours. This causes a great deal of inconvenience to the user.
Also, if copying of digital content is still permitted after the user acquires the digital content and records it to a recording medium, the user can freely copy or move the recorded digital content to another recording medium. However, in the case of digital content marked as “Copy one Generation”, once the user has acquired the digital content and recorded it onto some recording medium, the user cannot move that digital content to another recording medium. Since it is convenient to use a fixed recording medium such as an HDD that is easy to use and quick to access, the user is likely to record the acquired digital content first of all to such a fixed recording medium. However, fixed recording media have only limited capacities. Also, general fixed recording media such as HDDs are more susceptible to breakage than removable recording media, as they tend to be constantly used. For these reasons, if the user views the digital content and wants to store it long-term, it is desirable to move the digital content to a removable recording medium, such as a DVD-RW or a digital videotape, that has a larger capacity and is more preferable for long-term storage.
However, it is not acceptable, in terms of copyright protection, to alter the non-copyable status of the copyrighted digital content so as to improve user-friendliness.
Under copyright protection, digital content whose copy control information is “Copy Never” can be viewed but cannot be copied, whilst digital content whose copy control information is “Copy one Generation” can be copied only once.
In view of this, it is desirable to allow copying of digital content under a specific condition but then reliably nullify the digital content. In this way, user-friendliness can be improved without departing from the principle of copy prohibition.